The primary goal of this Scientific Conference is to advance the field of HIV-related medication adherence research through a review of methodological challenges and results of the initial wave of research on interventions to improve adherence to antiretroviral therapy. The conference will address adherence to HIV medications in general, while focusing in depth on drug users and other vulnerable populations of people living with HIV. Proceedings of the conference will be widely disseminated through publication in a Special Supplement of a major HIV/AIDS professional journal. Topics this conference will address include the relationship between biomedical and behavioral science in adherence research, challenges in the design of rigorous studies of adherence among drug users and other vulnerable populations, theoretical behavioral models in adherence intervention research, subject recruitment and retention, data management (with a special focus on managing the large data sets generated by measuring medication adherence), intervention dose, duration, fidelity, and durability and the special role of substance abuse treatment. The conference will also address the problems of translating new knowledge from research to practice: generalizability of findings, implementation in the community and clinic setting, cost effectiveness and reimbursement for adherence interventions, and implications for health policy. The conference will be held on the Yale University campus on June 9-10, 2005. Participants will be a multidisciplinary group of researchers and clinicians who are actively engaged in the study of adherence interventions among drug users and other vulnerable populations.